Mankind has been using ropes made from natural fibers for thousands of years. In addition, wire ropes and cables made from metallic filaments have been in use for hundreds of years. Because of the history of ropes, ropes, and cables, there is ambiguity about the precise definitions and uses of the terms rope, wire rope, cable. Traditionally, many people define ropes as being made from natural or polymeric fibers, wire ropes as being made from metallic filaments, and cables as being made from all of the above. Herein, the term "rope" refers to rope, wire rope and cable.
Almost any type of material which can be twisted, pulled, extruded, spun, stretched, or otherwise fabricated into a filament or fiber can be used to make ropes. Basically, a rope is a structural element which is fabricated from any collection of elongated members, such as filaments or fibers, which are manufactured into some type of a long, structural line which is relatively flexible and capable of carrying tensile loads.
A non-exclusive list of definitions of various elongated members used in ropes includes:
(a) Fiber--A natural or synthetic thread which is usually relatively short.
(b) Filament--A natural or synthetic thread which is usually relatively long.
(c) Wire--A filament which is usually drawn from pure or alloyed metals.
(d) Yarn--A group of twisted (spun or braided) fibers, filaments, and/or wires.
(e) Cord--A group of twisted (spun or braided) yarns.
(f) Strand--A group of twisted yarns or cords; typically, small diameter ropes will have its strands fabricated from yarns whereas larger ropes will use cords.
Most common ropes are manufactured by the following process:
(1) Relative short to moderately long filaments or fibers are twisted into yarns.
(2) Yarns are twisted into cords.
(3) Cords are twisted into strands. This process is called "forming." Sometimes, extra cords, yarns, and/or filaments (made from relatively flexible materials) are added during the forming process for internal lubrication in each strand. These extra cords, yarns, and/or filaments are commonly used during the fabrication of ropes that are subjected to relatively high flexural loads.
(4) Two or more strands are twisted into a rope. This process is called "laying." Similar to Step 3, extra strands, cords, yarns, and/or filaments (made from relatively flexible materials) can be added during the laying process to improve internal lubrication in the rope.
(5) Two or more ropes are twisted into a wire rope or cable. Similar to Step 4, extra elongated members can be added to improve internal lubrication in the cable.
Since each of the above manufacturing steps can have many different variations, there is almost an infinite number of different types of ropes which this basic process can produce. Common examples of some of the variations include:
(a) Varying the numbers of elongated members per rope.
(b) Using two or more different material types of elongated members per yarn.
(c) Varying the diameters of the elongated members.
(d) Varying the number of twists per unit length of the elongated members.
(e) Using different combinations or diameters of elongated members per rope.
(f) Varying the direction of rotation of one or more of the elongated members.
(g) Varying the direction of twists per unit length of one or more of the elongated members.
(h) Varying the number of extra elongated members for internal lubrication.
Many ropes have external materials applied to the yarns, cords, or strands to improve environmental resistance, as well as handling characteristics. Application processes for these materials include galvanizing, bonding, painting, and coating. Some typical examples of how the characteristics of a rope can vary by using these manufacturing variations include:
(a) Ropes that are made from thick filaments will be stiffer than ropes from thinner filaments.
(b) Ropes that use additional elongated members for internal lubrication will have improved bending capabilities and a longer service life than ropes which do not use extra elongated members for internal lubrication.
(c) Ropes that are made with the yarn twist in the opposite direction as the cord twist will have greater torsional stability than ropes with both twists in the same direction. Likewise, ropes that have their cord twist and strand twist in opposite directions will have greater torsional stability than ropes with both twists in the same direction. This rule is also true when the direction of the strand twist is opposite to the rope twist.
(d) Ropes which are fabricated with the strands twisted in the same direction as the overall rope twist direction have improved resistance to surface wear (due to a larger exposed surface area) than ropes which have the strand twist and a rope twist in opposite directions. In recent years, it has been discovered that stresses and strains on optical fibers change the way in which light is reflected and transmitted through the fiber. The type of stress or strain and the area of the fiber in which the stress or strain is being applied may be calculated or determined by monitoring the change in characteristics of reflected or transmitted light in the fiber.
Such fibers have been incorporated into laminated structures, commonly known as smart structures, the common characteristic to the earlier structures being their rigid (substantially inflexible) nature.